(1) Field of the Invention
The invention relates to a method of forming an improved MOSFET device structure for use in ultra large scale integration devices. A local self-aligned anti-punchthrough region is formed directly under the gate electrode using ion implantation. The anti-punchthrough region reduces the expansion of the depletion region in the channel and thereby increases the punchthrough voltage. The local anti-punchthrough region is self-aligned with the gate electrode and source/drain region so that critical spacings are maintained even for sub micron devices. The source and drain junction capacitances are also reduced. The invention can be used in either N channel or P channel MOSFET devices.
(2) Description of the Related Art
In using field effect transistors in the formation of ultra large scale integrated circuit devices device punchthrough has become an increasing problem. Punchthrough ion implantations have been used near the source and drain to reduce the depletion width in the channel thereby increasing the punchthrough voltage. These methods have had the problem of increasing the source and drain capacitance and reducing channel mobility. This invention provides new methods of forming a local anti-punchthrough implant region which is self-aligned with the source/drain implantations and the gate electrode. The local anti-punchthrough implant region maintains channel mobility and minimizes junction capacitance. Self-alignment maintains critical spacings helping to minimize source and drain junction capacitances.
Hot carrier reliability and performance of 0.15 micron CMOSFETs are discussed in a paper by Takeuchi et al, "0.15 um CMOS with High Reliability and Performance" in IEDM, November 1993, Pages 883-886. Non uniformly doped channels are discussed in a paper by Okumura et al, "Source-to-Drain Nonuniformly Doped Channel (NDUC) MOSFET Structures for High Current Drivability and Threshold Voltage Controllability," IEEE Transactions on Electron Devices, Vol 39, No. 11, November 1992, Pages 2541-2552.